Scale lamp threads

[brightsparkey]

I've been having a-lot of trouble with scale lamps. I had issues with lamps on my Grundig set, and now on my SABA Dorchester too. I'm starting to suspect that there is some confusion to do with lamp types that I'm not aware of, and wondered if anyone can shed a little light - no pun intended.

I've purchased "scale lamps, MES, E10" from two different ebay sellers. In both cases I think the lamps are basically from the same source. They almost fit the lamp holders in the above radios, but are too loose to grip when tightened and slip thread.

I also purchased some MES lamp holders when trying to sort out my Grundig which are modern lamp holders of the clear plastic variety designed to spade mount on the side - they are remarkably similar to the SABA lamp holders on the Dorchester. Said lamps _do_ fit into these holders OK. The original lamp also fits but is rather tight..

I think this means they are MES, but is that the same as E10 and are the original scale lamps MES, E10 or something different?

I've attempted to photo the lamps - original and new (fairly obvious which is which..) the pitch of the thread is similar but somehow the angle of the thread looks different...

Kevin.

[Station X]

As far as I know Edison threads and E threads are the same thing. The figure following the E denotes the diameter measured over the crests of the thread. So E10 is 10mm.

[paulsherwin]

The screw pitch / helix angle certainly looks different to me. Maybe the German manufacturers were using some local standard rather than E10. I've not come across this but I rarely see German sets.

[Station X]

The other standard I know of is for 'T' type lamps. Here the figure after the T has to be multiplied by 1/8" to give the diameter. So T T3.25 lamp has a diameter of about 10.3 mm.

[brightsparkey]

I measured the outside diameter with the very-nears..

Old Lamp 9.35mm
New Lamp 9.2mm

Not entirely conclusive..

Just checked the service manual which calls for an 'E10' lamp.

[Aerodyne]

Not entirely conclusive, true... but 1.15mm over a total diameter of less than 10mm is a big error, if error it is. It certainly explains the lack of grip with the new lamps. You could try a 'bodge' with some fine solid-core copper wire wrapped a time or two around the threads of the new lamps or, failing that, could you use a jewellery saw (piercing saw, very fine blade) to cut so far down the holder to nip it in slightly? Admittedly a tricky task. This is assuming no further supply of the exact correct lamps can be found.

Tony

[John M0GLN]

From the Machinery's screw thread book the sizes for an Edison E10 thread are,

major dia of cap is 9.53 - 9.36mm
major dia of socket is 9.78 - 9.61mm
minor dia od of cap is 8.51mm
minor dia of socket is 8.76 - 8.59

and the pitch is 1.814mm

so I presume by cap they mean the male screwed end which you have measured as 9.35 and 9.2mm, not that far out if the pitch is the same.

John

[Station X]

I checked a few ancient examples of MES/E10 and they're all around 9.4mm OD. ie within the tolerance quoted in the previous post.

New unused examples, made in China, were around 9.2mm OD. ie out of tolerance.

[broadgage]

I have purchased some NOS lamps from Russia and they are smaller than the norm and a poor fit in some holders.

Quality seems to vary a lot, I also have some NOS pifco torch bulbs that have very poorly formed threads and won't fit some modern holders.

Imports from outside western Europe or the USA seem to be of doubtful quality whether recent or from decades ago.

I recently purchased some 2.5v 0.06a E10 lamps with good threads, made in Germany I think.

[brightsparkey]

Once again, excellent info from John. Thanks to all - my conclusion is the lamps are at fault and I should look again for another supplier <sigh>.

I now have 20 lamps with no home - new fairy light project?

In the process, hacking around the web for info , I came across a few pics someone has put on the radiomuseum site of a Grundig set's holder - mounted at 90 degrees to my sets' - so it looks like the previous bodger/owner had bent round the spade to accommodate their incorrect holders thus leading me astray.. there's always a silver lining - one more mystery possibly solved.

Thanks,

Kevin.

[Herald1360]

A small smear of solder on the threads of the new bulbs may up the diameter enough for the holder to grip. You may heed to file through the shiny plating to get it to tin.

[Ambientnoise]

Would winding a strip of aluminium foil around the thread work ?

Ken

[Philips210]

Hi.

I too have experienced this over twenty years ago. When I inspected the threads of the poorly fitting bulb, I noticed that although the pitch looked correct, the depth of the thread looked shallow compared to the decent one. I didn't bother using them and found some good alternatives.

CPC used to supply quite a range of bulbs branded VCH and they seemed well made. Shame that brand's not stocked any more though they do have a limited stock of other suppliers' bulbs.

Regards
Symon.

[McMurdo]

VCH are now known as CML, their factory is still in Bury St Edmonds. CPC/Farnell stock them.

https://www.cml-it.com/en/products/l...ent-lamps-28mm

[Philips210]

Thanks Kevin, that's useful to know.

Regards
Symon